Well, yeah it's very obvious Kishi is holding back Sasuke for something big. Sasuke hasn't went all out since his fight with Danzo which was hundreds of chapters ago. Ever since his fight with Danzo, he's been overshadowed by everyone. First with Itachi and Kabuto, then with Orochimaru and The Hokages and now with Obito and Madara. It's so obvious Kishi is holding him back for something.
While we haven't seen EMS Sasuke go all out, I do think he's going to get a power up.
There's either two scenarios I want to see
1) He stays with EMS, just unlocks its full potential
Perfect Susanno (Enton Coated) - He'll learn to stabilize his Susanno in battle. He awakened higher stages of Susanno in previous battles and it'll be the same for perfect Susanno.
Yata Mirror and Totsuka Sword - He has Itachi's eyes and can apparently feel his power flowing through him. I think Itachi gave the weapons to Sasuke to protect him before he left as an Edo.
Unique NEW EMS Power - The Jutsu that Itachi spoke of.
2) He unlocks the Elder Son's eyes. We find out that they're actually stronger then the Rinnegan which is not impossible. Sometimes evolutions are stronger then the originals. Besides, Kishi could find a way to explain why nobody else knows about the eye therefore not being included when Rinnegan was called the strongest eye.